Please be sure to check your State Statutes regarding self-defense and duty to retreat before reading any of my rambles
In this case, the only variables I could fathom would be if the assailant was within
a few feet of his door and verbally indicated an intention to retrieve a firearm or other deadly weapon, then turned and went for it. Your case has a better chance if you acted with deadly force to terminate his perceived immediate threat. As in, "If I didn't fire, he would have got to his (Insert deadly weapon).
There is some understanding if you can properly... I mean very properly articulate your fear of death or great bodily harm. If he was a chasing distance away (4 or 5 yards) from you and/or the car, it's probably not going to put you in immediate harm, but enough to at least draw to low-ready or up on target in anticipation, depending on your level of fear.
I wouldn't give chase to position for a better point blank shot, but if you can run towards him, you could also likely run for cover/conclmnt. Showing at least some attempt to get away from the aggressor. Or just draw and stand your ground (depending on your state).
I personally find it bothersome that states are inconsistent with allowing their citizens to stand their ground. I'd hate to go on vacation to find myself in a situation where I'm trying to remember others' SD laws.
Also, notify PD ASAP, since in a few minutes, you might walk into some deputies mentioning something about a Sunday School teacher and his bible study girlfriend stopping to ask directions for the local Hebrew School when this crazy man with a puppy and a .45 tried to kill them.
That's why I just use..."High Karate!"